1. Field of the Invention
The present invention relates to a spin injection magnetization reversal type magnetic random access memory (MRAM).
2. Description of the Related Art
Recently, a spin injection magnetization reversal type magnetic random access memory (e.g., non-patent reference 1) is proposed as a magnetic random access memory (MRAM). A cell of this magnetic random access memory comprises an MTJ (Magnetic Tunnel Junction) element and switching transistor. In a write operation using the spin injection magnetization reversing technique, an electric current is supplied perpendicularly to the film surface of the MTJ element, and the magnetization direction in a recording layer is changed by the direction of this electric current.
Unfortunately, in a one transistor+one MTJ type memory cell of the spin injection magnetization reversal type magnetic random access memory, if a common interconnection (common source line) shared by another cell on the transistor side and a common interconnection (bit line) shared by another cell on the MTJ side are perpendicular to each other, all unselected bit lines must be charged to a predetermined potential in a write cycle. This decreases the operating speed.
To solve the above problem, it is possible to form the common source line and bit line parallel to each other. In this case, the common source line runs between bit lines, and MTJ elements are formed below the bit lines. Consequently, a contact connecting each MTJ element and a drain diffusion layer is formed close to the common source line. In order to prevent this, the cell size cannot be made smaller than 8 F2.
[Non-patent Reference 1] IEDM2005 Technical Digest p. 473-476 “A Novel Nonvolatile Memory with Spin Torque Transfer Magnetization Switching: Spin-RAM” or J. of Magn. Magn. Mater., 159, L1(1996) “Current-driven excitation of magnetic multilayers”